tlbe S&B anfc its Colon 145 



There are other optical effects to be seen 

 sometimes on the horizon somewhat resem- 

 bling twilight. The " aurora borealis " (north- 

 ern lights), which we describe in Vol. III., is 

 seen in the northern skies at certain times, 

 and has very much the appearance of twilight 

 in some of its phases. It is constantly chang- 

 ing, however, and is easily distinguished by 

 anyone who has observed both. These ap- 

 pearances are undoubtedly electrical. There 

 is another phenomenon seen in the arctic 

 regions that causes a band of white light to 

 appear on the horizon called " ice blink," and 

 it is caused by the reflections from the great 

 icebergs that abound in that region. 



Curious optical effects are sometimes ob- 

 served a little after sunset in the form of 

 streamers or bands of light that shoot up into 

 the sky, sometimes to a great height. These 

 are undoubtedly due to cloud obstructions that 

 partially shut off the sun's rays from a part of 

 the sky, but allow it to shine with greater bril- 

 liancy in the path of these bands of light. 



It will be seen from the foregoing that the 

 sky in all of its phases is a product of sunlight 

 and the substances that float in the air, in- 

 cluding moisture, not only in the invisible 

 state, but in all the stages of condensation, as 

 well as particles of floating dust. 



